Audemars Piguet Royal Oak Concept GMT Tourbillon Instructions For Use Manual - page 7
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Time zones follow political borders
1. Intr
oduction
Eng
lish
Times-zones
The Earth's rotation means that true local time changes
at the least movement to the East or West. A worldwide
system of meridians at 15° intervals has therefore
been adopted to measure the average local time. The
Earth has thus been divided into 24 time zones, with
the central meridian in the middle.
This system was adopted during the international
conference in Washington in 1884 and Greenwich was
chosen as the Earth's prime meridian. The meridian
passing through Greenwich in Great Britain was chosen
as the prime meridian, i.e. the reference axis for
Coordinated Universal Time (UTC or GMT) on which all
time zones would be based.
Thus you have to put your watch forward by one hour
when crossing from one time zone to the next going
East. Put your watch back by one hour when crossing
from one time zone to the next going West.
Theoretically, all of the points on the globe with the
same longitude should be in the same time zone. In
reality, each country has defined its time zone(s) as a
function of political borders, among other considerations
(see the map of time zones based on political borders).